It is known that a resin composite material having electrical conductivity or thermal conductivity can be prepared by blending a carbon filler such as carbon black, filamentous carbon and the like, a metal filler such as metal powder and the like, with a matrix material of a thermosetting resin or a thermoplastic resin.
Electrically conductive resin composite materials are expected to be used in the fields of, for example, electrostatic discharge (ESD) and electromagnetic wave shielding. However, resin composite materials containing conventional carbon fillers can merely have electrical conductivity of a volume resistivity of about 1×106 Ω·cm. Consequently, it can be used only in the fields where even low electrical conductivity is acceptable, such as antistatic materials and ESD protective elements, and cannot be practically used in the fields where high electrical conductivity is required, such as electromagnetic wave shielding materials.
A carbon nanotube is known as a carbon filler. The carbon nanotube can be produced by, for example, chemical vapor deposition (hereinafter, referred to as CVD). In the CVD, a carbon nanotube is produced using a catalyst generated by decomposing an organic metal complex, a metal salt, or the like in a gas phase reaction system or using a catalyst introduced into a gas phase reaction system in a colloidal state (Patent Literatures 1 to 3); or a carbon nanotube is produced using a supported type catalyst prepared by supporting catalyst particles on a carrier (see Patent Literature 7 or Non-Patent Literature 1).
Carbon fibers produced by the former method using an organic metal complex or the like tend to have defects in the graphite layers. Accordingly, graphitization by heating the resulting carbon fibers at high temperature is necessary to obtain an effect as an electrically conductive filler.
The latter method using a supported type catalyst includes a method of using a basal plate (substrate method: see Patent Literatures 4 to 6) and a method using a powder-like carrier. In the substrate method, carbon nanotubes are generated on a basal plate carrying a catalyst. In order to produce a large amount of carbon nanotubes by the substrate method, a large number of basal plates are required, resulting in low efficient productivity. In addition, it is necessary to collect the generated carbon nanotubes from the basal plates, resulting in an increase in number of steps uneconomically. Accordingly, the substrate method has not been industrially used yet.
In contrast, the method using a powder-like carrier can secure a large surface area even in a small volume and therefore has high efficient productivity. As the powder-like carrier, fine powder having a large specific surface area, such as alumina, magnesia, silica, or zeolite, has been generally used. In the carbon nanotubes prepared by the conventionally used powder-like supported-type catalyst, however, a composite material having desired high electrical conductivity cannot be obtained by adding a small amount of the carbon nanotubes to a resin. In order to obtain a composite material having high electrical conductivity, it is necessary to blend a large amount of the carbon nanotubes with a resin. A resin blended with a large amount of carbon nanotubes, however, notably loses excellent characteristics intrinsically possessed by the resin.